1. Field of the Invention
The invention is related to the field of earth boring tools, and in particular rotating drag bits having large polycrystalline diamond compact cutters or other large composite-type cutters of similar materials for use in drilling in shale, clay and other sticky formations, sometimes referred to as "gumbo".
2. Description of the Prior Art
One of the most significant problems encountered when drilling in shale, clay or other water reactive, sticky formations is the tendency of the bits to ball or become clogged during drilling. The typical approach of the prior art in dealing with such soft and sticky formations has been to provide large cutters with strong hydraulics in the proximity of the cutters and to attempt to remove the cuttings from the cutter faces with a high volume, high velocity hydraulic jet flow. See, for example, Feenstra, "Rotary Bit with Ridges", U.S. Pat. No. 4,116,289 (1978).
Typically, such prior art cutters include impregnated diamond blade cutters, sintered diamond compact cutters, such as manufactured by General Electric Co. under the trademark "Compax", are limited in size, typically being equal to or less than 13.3 mm in diameter. Therefore, in order to obtain the cutter sizes required or desirable for sticky drilling, impregnated diamond elements are used such as shown by Short, "Blade-Type Drill Bit", U.S. Pat. No. 3,153,458 (1964), and Feenstra, supra.
Recently, however, large size diamond compact discs have become commercially available measuring between three quarters of an inch and two inches in diameter. However, these large diamond discs have been employed essentially as their smaller predecessors, such as diamond stud cutters sold under the trademark "Stratapax" by General Electric Company. As a result, the large diamond discs have been subject to the same drawbacks and detriments with respect to cutting sticky or plastic or water reactive formations as prior art blade bits.
Therefore, what is needed is some means whereby the large diamond cutter may be employed to cut into clay, shale or plastic formations in such a manner that bit balling and other drawbacks of the prior art are substantially avoided.